A transmission system comprising a tool comprising an annular groove. An inductive coupler comprising a housing disposed within the annular groove, and an annular MCEI trough within the housing. An annular coil wire being laid within the annular MCEI trough; the coil wire being connected to coaxial cable within the tool. The coaxial cable comprising a mesh reinforced polymeric composite dialectic material intermediate a center electrical conductor and an outer electrically conducting sheath. The dialectic material comprising MCEI fibers in sufficient volume to capture an electromagnetic field surrounding the center conductor and shield a signal being transmitted along the center conductor from outside electromagnetic interference. The center conductor may run through MCEI mesh reinforced beads embedded within the dialectic material. The coaxial cable may extend within the tool or to the opposite end of the tool with the center conductor being connected to a similarly configured inductive coupler.
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1. An inductively coupled transmission system, comprising:
a drill string tool comprising inductive couplers disposed at opposite ends of the drill string tool;
the inductive couplers each comprising an annular magnetically conducting electrically insulating (MCEI) trough within an annular housing disposed within an annular groove and an electrically conductive coil mounted within the annular MCEI trough, respectively;
the electrically conductive coil connected to a coaxial cable running between the inductive couplers at the opposite ends of the drill string tool;
the coaxial cable comprising a cylindrical coaxial composite polymeric dielectric material intermediate a center electrical conductor and an electrically conductive outer sheath along its length;
the cylindrical coaxial composite polymeric dielectric material comprising magnetically conducting electrically insulating (MCEI) fibers suspended within the cylindrical coaxial composite polymeric dielectric material of the coaxial cable.
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This application is a modification of U.S. Pat. No. 7,064,676, to Hall et al., entitled Downhole Data Transmission System, issued Jun. 20, 2006, incorporated herein by this reference. The (Prior Art)
This application is also a modification of U.S. Pat. No. 6,982,384, to Hall et al., entitled Load-Resistant Coaxial Transmission Line, issued Jan. 3, 2006, incorporated herein by this reference. The (Prior Art)
(Prior Art)
The present invention relates to the field of data transmission systems, particularly data transmission systems suitable for use in downhole environments, such as along a drill string used in oil and gas exploration, or along the risers and casings and other equipment used in oil and gas production.
The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc.
Briefly stated, the invention is a system for transmitting data through drill string components.
An inductively coupled transmission system for tools that may be used in a drill string comprising a drill string tool comprising an inductive coupler. The inductive coupler may be disposed within an annular groove or recess in the body of the drill string tool. The drill string tool may be attached to drill rig equipment, a top drive, a drill pipe, a riser, a sub, a bottom hole assembly, or a drill bit. The inductive coupler may be in communication with to drill string sensors, mud-pulse equipment, electromagnetic transceivers, and acoustic transmitters and receivers. The inductive coupler may comprise an annular magnetically conductive electrically insulating, MCEI, trough or channel within an annular housing, and an electrically conductive coil may be mounted within the MCEI trough. The MCEI trough and fibers described herein may be comprised of ferrite. The electrically conductive coil may be connected to a coaxial cable. The coaxial cable may comprise a composite polymeric dielectric material intermediate a center electrical conductor and a sheath, the sheath may be electrically conducting. The sheath my comprise a stainless steel tube. The stainless steel tube may be non-magnetic. The stainless steel tube may be coated with a wear resistant coating suitable for the downhole environment. The polymeric dielectric composite material may comprise minute MCEI fibers suspended within the polymer.
The composite polymeric dielectric material may comprise an open mesh reinforcement embedded within the dielectric material. The open mesh reinforcement may act as an electromagnetic shield. The open mesh may act to prevent the propagation of an electromagnetic field surrounding the center conductor within the coaxial cable. The mesh may also prevent stray electromagnetic interference from outside the coaxial cable to affect the data transmission along the cable. The open mesh may be metal or non-metal and may be electrically conductive or non-conductive. The open mesh may transmit pressure from the sheath through the dielectric material to the center conductor. It may be desirable that the components of the coaxial cable move in unison as the gravitational forces are increased on the coaxial cable along the drill string as it is deployed downhole. Gravitational forces on the drill string may cause the components of the drill string to stretch or elongate during deployment. Not only may the repeated stretching of the coaxial components sever the components, also it may cause the components to abrade and wear out prematurely. In order to resist the effects of the gravitational forces, it may be desirable to compress the coaxial cable, putting the components in sufficient compression to prevent independent movement and elongation. The open nature of the mesh may promote the transmission of pressure from the outer sheath through the dielectric material onto the center conductor. The compressed condition of the cable's components may allow them to move in unison in a deployed drill string.
The MCEI fibers suspended within the polymer may be in sufficient volume to capture an electromatic field emanating from the center electrical conductor and shield a power and data signal being transmitted along the center conductor from outside electromagnetic interference. The MCEI fibers suspended within the polymeric dielectric material may comprise between 3% and up to 73% by volume of micron and submicron fibers of Fe and Mn ranging in average diameters of between 150μ and 3000μ in an average ratio of between 8:2 and 2:8, respectively. Other fibers comprising transition metals and oxygen may be combined and added to the dielectric material in order to achieve a desired shield for the transmission of data and power along the center conductor of the coaxial cable. The fibers may comprise ferrite fibers in sufficient volume to eliminate or reduce the electromagnetic interference of the signal along the center conductor.
The center electrical conductor may pass through an axial passageway in elastically deformable open mesh reinforced polymeric MCEI beads positioned along the center conductor within the coaxial cable assembly. The reinforced polymeric MCEI beads may be assembled along the center conductor end for end or they may be spaced apart. The beads may be interlocking. The elastically deformable nature of the beds may allow the beads to compress with the other components of the coaxial cable. The compressive state of the components may allow the components to move in unison as the cable reacts to the gravitational elongation of the drill string when it is deployed downhole. Like the dielectric material, itself, the MCEI beads may comprise an open mesh embedded within the beads. The open mesh may allow the pressures within the coaxial cable to act on the center conductor uniformly with the other components of the coaxial cable. And the beads may comprise MCEI fibers in sufficient volume to capture the electromagnetic field produced by the center conductor when it is energized and may act as a shield against outside electromagnetic interference on a signal transmitting along the center conductor.
The annular housing may comprise a polymeric block comprising MCEI fibers. The annular housing may be similar to the annular housing shown in (Prior Art)
The open mesh reinforcement used in the polymeric dielectric composite material and polymeric beads may comprise a metallic wire, a carbon fiber, a glass fiber, or a nylon or rayon fiber mesh reinforcement. The open mesh may or may not be electrically and magnetically conductive. The open mesh may at least partially envelop the dielectric composite material and the polymeric beads rather than be embedded therein. The open mesh may be isolated from the other components of the coaxial cable assembly.
The annular recess or groove may be similar to that shown in (Prior Art)
The following portion of the summary is taken from the '676 reference. The descriptions pertain to
The object of the present invention is to provide a highly reliable communications system for power transmission and for sending and receiving data along a drill string. This is achieved by means of an electromagnetic inductive coupler capable of power transmission and of transmitting and receiving a low power, high frequency, multiplexing carrier signal of greater than 10 kilobaud along the length of the drill string. In this manner, information on the sub-terranean conditions encountered during drilling and on the condition of the drill bit and other drill-string components may be communicated to the technicians located on the drilling platform. Furthermore, technicians on the surface may communicate directions to the drill bit and other downhole devices in response to the information received from the sensors, or in accordance with the pre-determined parameters for drilling the well.
The coupler consists of a means for producing an electro-magnetic field positioned within the tool joints of each section of drill pipe. Within the pipe sections, the couplers are connected by means of a conductor medium attached within the wall of the pipe bore. A low-wattage power source is provided and is placed in communication with at least one of the couplers. When the pipe sections are joined together, the respective couplers are in sufficiently close proximity that they share and electromagnetic field capable of transmitting power and sending and receiving the carrier signal. Without the aid of an additional power source or repeater to boost the signal, the signal may be transmitted along the conductor at least across the next joint. In this manner power and data may be transmitted along the entire drill string.
Another object of this invention is to provide a power and carrier signal that is resistant to the flow of drilling fluid, drill string vibrations, and electronic noise associated with drilling oil, gas, and geothermal wells.
Another object of this invention is to transmit and receive a carrier signal across several lengths of drill pipe without the aid of repeaters and additional electronic circuitry. This reduces the complexity of the communication system and increases its reliability.
Another object of this invention is to provide a coupler that is transparent to make up methods employed on the drilling platform, as well as maintenance procedures employed in re-machining the tool joints.
In accordance with one aspect of the invention, the system includes a plurality of downhole components, such as section of pipe in a drill string. Each component has a first end and a second end, the first end of one downhole component being adapted to be connected to the second end of another downhole component.
Located proximate to the first end is a first magnetically conductive, electrically insulating element. This element includes a first U-shaped trough with a bottom, first and second sides and an opening between the two sides. A second magnetically conductive, electrically insulating element is located proximate the second end of each downhole component. This second element likewise includes a second U-shaped trough with a bottom, first and second sides and an opening between the two sides. The first and second troughs are configured so that the respective first and second sides and openings of the first and second troughs of connected components are substantially proximate to and substantially aligned with each other.
A first electrically conducting coil is located in each first trough, while a second electrically conducting coil is located in each second trough.
An electrical conductor is in electrical communication with and runs between each first and second coil in each component.
In operation, a varying current applied to a first coil in one component generates a varying magnetic field in the first magnetically conductive, electrically insulating element, which varying magnetic field is conducted to and thereby produces a varying magnetic field in the second magnetically conductive, electrically insulating element of a connected component, which magnetic field thereby generates a varying electrical current in the second coil in the connected component.
In accordance with another aspect of the invention, the system includes a plurality of downhole components, each with a pin end and a box end. Each pin end includes external threads tapering to a pin face, while each box end includes internal threads tapering to a shoulder face within the box end. The pin face and shoulder face are aligned with and proximate each other when the pin end of the one component is threaded into a box end of the other component. A first inductive coil located within a recess formed in each pin face, while a second inductive coil located within a recess formed in each shoulder face. An electrical conductor is included which is in electrical communication with and runs between each first and second coil in each component.
In accordance with another aspect of the invention, the system includes a plurality of downhole components, each with a first end and a second end, the first end of one downhole component being adapted to be connected to the second end of another downhole component. A first electrically conducting coil having no more than five turns, and preferably no more than two, most preferably no more than one, is placed at each first end, while a second electrically conducting coil having no more than five turns, and preferably no more than two, most preferably no more than one, is placed at each second end. The first and second coils of connected components are configured so as to be substantially proximate to and substantially aligned with each other. An electrical conductor is provided which is in electrical communication with and runs between each first and second coil in each component. In operation, a varying current applied to a first coil in one component generates a varying magnetic field, which magnetic field induces a varying electrical current in the second coil in the connected component, to thereby transmit a data signal.
In accordance with another aspect, the invention is a downhole tool adapted to transmit data over the systems described above.
The present invention provides the advantage that, as the data transmission line uses alternating conductive and inductive elements, the inductive elements at the end of each segment enable the transmission line to be lengthened or shortened during drilling operations without need for an electrically conductive path across the joint. Indeed, the only closed electrical path is within each individual element, which constitutes a single closed path for electrical current.
It should be noted that, as used herein, the term “downhole” is intended to have a relatively broad meaning, including such environments as drilling in oil and gas, gas and geothermal exploration, the systems of casings, risers, and other equipment used in oil, gas and geothermal production.
It should also be noted that the term “transmission” as used in connection with the phrase data transmission or the like, is intended to have a relatively broad meaning, referring to the passage of signals in at least one direction from one point to another.
It should further be noted that the term “magnetically conductive” refers to a material having a magnetic permeability greater than that of air.
It should further be noted that the term “electrically insulating” means having a high electrical resistivity, preferably greater than that of steel.
The present invention, together with attendant objects and advantages, will be best understood with reference to the detailed description below in connection with the attached drawings.
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The following detailed description is in relation to
An inductively coupled transmission system for tools that may be used in a drill string comprising a drill string tool comprising an inductive coupler. The inductive coupler may be disposed within an annular groove or recess in the body of the drill string tool. The drill string tool may be attached to drill rig equipment, a top drive, a drill pipe, a riser, a sub, a bottom hole assembly, or a drill bit. The inductive coupler may be in communication with drill string sensors, mud-pulse equipment, electromagnetic transceivers, and acoustic transmitters and receivers. The inductive coupler may comprise an annular magnetically conductive electrically insulating, MCEI, trough or channel within an annular housing, and an electrically conductive coil may be mounted within the MCEI trough. The MCEI trough and fibers described herein may be comprised of Ferrite. The electrically conductive coil may be connected to a coaxial cable, a segment which is represented in
The composite polymeric dielectric material 315 may comprise an open mesh 320 reinforcement embedded within the dielectric material 315. The open mesh 320 reinforcement may act as an electromagnetic shield. The open mesh 320 may act to prevent the propagation of an electromagnetic field surrounding the center conductor 325 within the coaxial cable 300. The mesh 320 may also prevent stray electromagnetic interference from outside the coaxial cable 300 to affect the data transmission along the center conductor 325. The open mesh 320 may be metal or non-metal and may be electrically conductive or non-conductive. The open mesh 320 may transmit pressure from the sheath 305 through the dielectric material 315 to the center conductor 325. It may be desirable that the components 305, 315, 325, 330, and 340 of the coaxial cable 300 move in unison as the gravitational forces are increased on the coaxial cable 300 along the drill string as it is deployed downhole. Gravitational forces on the drill string may cause the components 305, 315, 325, 330, and 340 of the drill string to stretch or elongate during deployment. Not only may the repeated stretching of the coaxial components 305, 315, 325, 330, and 340 sever the components 305, 315, 325, 330 and 340, also it may cause said components to abrade and wear out prematurely. In order to resist the effects of the gravitational forces, it may be desirable to compress the coaxial cable 300, putting the components 305, 315, 325, 330. And 340 in sufficient compression to prevent independent movement and elongation. The open nature of the mesh 320 may promote the transmission of pressure from the outer sheath 305 through the dielectric material 315 onto the center conductor 325. The compressed condition of the cable's 300 components 305, 315, 325, 330. And 340 may allow them to move in unison in a deployed drill string.
The MCEI fibers suspended within the dielectric polymer 315, 335 may be in sufficient volume to capture an electromatic field emanating from the center electrical conductor 325 and shield a power and data signal being transmitted along the center conductor 325 from outside electromagnetic interference. The MCEI fibers suspended within the polymeric dielectric material 315, 335 may comprise between 3% and up to 73% by volume of micron and submicron fibers of Fe and Mn ranging in average diameters of between 1501μ and 3000μ in an average ratio of between 8:2 and 2:8, respectively. Other fibers of transition metals and oxygen may be combined and added to the dielectric material in order to achieve a desired shield for the transmission of data and power along the center conductor 325 of the coaxial cable 300. The fibers may comprise ferrite fibers in sufficient volume to eliminate or reduce the electromagnetic interference of the signal along the center conductor 325.
The center electrical conductor 325 may pass through an axial passageway in elastically deformable open mesh 320, 345 reinforced polymeric MCEI beads 330, 340 positioned along the center conductor 325 within the coaxial cable assembly 300. The reinforced polymeric MCEI beads 330, 340 may be assembled along the center conductor 325 end for end or they may be spaced apart. The beads 340 may be interlocking. The elastically deformable nature of the beads 330, 340 may allow the beads 330, 340 to compress with the other components 305, 315, and 325 of the coaxial cable. The compressive state of the components 305, 315, 325, and 340 may allow the components 305, 315, 325, 330, and 340 to move in unison as the cable 300 reacts to the gravitational elongation of the drill string when it is deployed downhole. Like the dielectric material 315, 335, itself, the MCEI beads 330, 340 may comprise an open mesh 320, 345 embedded within the beads 330, 340. The open mesh 320, 345 may allow the pressures within the coaxial cable 300 to act on the center conductor 325 uniformly with the other components 305, 315, 325, 330 and 340 of the coaxial cable 300. And the beads 330, 340 may comprise MCEI fibers in sufficient volume to capture the electromagnetic field produced by the center conductor 325 when it is energized and may act as a shield against outside electromagnetic interference on a signal transmitting along the center conductor 325.
The annular housing may comprise a polymeric block comprising MCEI fibers. The annular housing may be similar to the annular housing shown in (Prior Art)
The open mesh 320, 345 reinforcement in the polymeric dielectric composite material 315 and polymeric beads 335 may comprise a metallic wire, a carbon fiber, a glass fiber, or a nylon or rayon fiber mesh 320, 345 reinforcement. The open mesh 320, 345 may or may not be electrically and magnetically conductive. The open mesh 320, 345 may at least partially envelop the dielectric composite material 315 and the polymeric beads 335 rather than be embedded therein. The open mesh 320, 345 may be isolated from the other components 305, 315, 325, and 330 of the coaxial cable 300 assembly.
The annular recess or groove may be similar to that shown in (Prior Art)
(Prior Art)
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The electromagnetic couplers may be axially stacked within the bore of the pipe as a means for accommodating maintenance of the tool joints. As the pipes are assembled and disassembled, shoulders 27A and 29A will often become damaged. These shoulders are the primary seal for the pipe joint, and a leak at the joint may cause a “wash out” and catastrophic failure of the joint, itself. Therefore, it is necessary to re-machine the sealing surface of the joint, resulting in a change of length of pin and box ends. In order to compensate for the change in length, the internal shoulder housing the electromagnetic coupler may also have to be re-machined. In a staked configuration, the outside coupler may be machined away to compensate for the change of length of the tool joint and fresh coupler exposed in its place. Normally, three re-machinings of the pipe joint are allowed before the threads must be recut. Therefore, a stack of three couplers may be provided in each joint as a means for allowing for the maintenance of the joint without having to reinstall the entire system. Another method that would accommodate maintenance of the tool joints would be to provide for a mechanical connector between the coupler and the shoulder of the groove. The attached conductor means could then be permanently attached to the female side of the connector and the coupler could be attached to the male side. The female side of the coupler could be of a sufficient width to allow for re-machining. Then, when maintenance of the tool joints is required, the coupler could be removed, the joints along with the female side of the connector re-machined, and the couplers reinstalled.
(Prior Art)
These small batteries may also be installed within the drill pipe wall, or within the wall of a specially designed sub assembly, without materially affecting the strength of the pipe.
Referring to the drawings, (Prior Art)
(Prior Art)
The data transmission system of the present invention may also be used with the casings, sensors, valves, and other tools used in oil and gas, or geothermal production.
The depicted section 11 includes a pin end 13, having external tapered threads 15 (see (Prior Art)
There are several designs for the pin and box end of drill pipe. At present, the most preferred design to use with the present invention is that which is described in U.S. Pat. No. 5,908,212 to Grant Prideco, Inc. of Woodlands, Tex., the entire disclosure of which is incorporated herein by reference. As shown in (Prior Art)
An alternate design for the pin and box end is disclosed in U.S. Pat. No. 5,454,605, assigned to Hydrill Company, Houston, Tex. As seen in (Prior Art)
As shown in (Prior Art)
Preferably, the recess is machined into the face by conventional tools either before or after the tool joint is attached to the pipe. The dimensions of the recess can be varied depending on various factors. For one thing, it is desirable to form the recess in a location and with a size that will not interfere with the mechanical strength of the pin end. Further, in this orientation, the recesses are located so as to be substantially aligned as the joint is made up. Other factors will be discussed below.
As can be seen in these figures, the recess is preferably configured so as to open axially, that is, in a direction parallel to the length of the drill string. In an alternative embodiment shown in (Prior Art)
A typical drill pipe alloy, 4140 alloy steel, having a Rockwell C hardness of 30 to 35, has a magnetic permeability of about 42. The magnetic permeability of a material is defined as the ratio of the magnetic flux density B established within a material divided by the magnetic field strength H of the magnetizing field. It is usually expressed as a dimensionless quantity relative to that of air (or a vacuum). It is preferably to close the magnetic path that couples the adjacent coils with a material having a magnetic permeability higher than the steel. However, if the magnetic material is itself electrically conducting, then they provide an alternate electrical path to that offered by the adjacent loops. The current thus generated are referred to as eddy currents; these are believed to be the primary source of the losses experienced in prior-art transformer schemes. Since the magnetic field is in a direction curling around the conductors, there is no need for magnetic continuity in the direction of the loop.
In the preferred embodiment illustrated in (Prior Art)
One property of the MCEI element is that it is magnetically conducting. One measure of this property is referred to as the magnetic permeability discussed above. In general, the magnetically conducting components should have a magnetic permeability greater than air. Materials having too high of a magnetic permeability tend to have hysteresis losses associated with reversal of the magnetic domains themselves. Accordingly, a material is desired having a permeability sufficiently high to keep the field out of the steel and yet sufficiently low to minimize losses due to magnetic hysteresis. Preferably, the magnetic permeability of the MCEI element should be greater than that of steel, which is typically about 40 times that of air, more preferably greater than about 100 times that of air. Preferably, the magnetic permeability is less than about 2,000. More preferably, the MCEI element has a magnetic permeability less than about 800. Most preferably, the MCEI element has a magnetic permeability of about 125.
In order to avoid or reduce the eddy currents discussed above, the MCEI is preferably electrically insulating as well as magnetically conductive. Preferably, the MCEI element has an electrical resistivity greater than that of steel, which is typically about 12 micro-ohm cm. Most preferably, the MCEI has an electrical resistivity greater than about one million ohm-cm.
The MCEI element 27 is preferably made from a single material, which in and of itself has the properties of being magnetically conductive and electrically insulating. A particularly preferred material is ferrite. Ferrite is described in the on-line edition of the Encyclopedia Britannica as “a ceramic-like material with magnetic properties that are useful in many types of electronic devices. Ferrites are hard, brittle, iron-containing, and generally gray or black and are polycrystalline—i.e., made up of a large number of small crystals. They are composed of iron oxide and one or more other metals in chemical combination.” The article on ferrite goes on to say that a “ferrite is formed by the reaction of ferric oxide (iron oxide or rust) with any of a number of other metals, including magnesium, aluminum, barium, manganese, copper, nickel, cobalt, or even iron itself” Finally, the article states that the “most important properties of ferrites include high magnetic permeability and high electrical resistance.” Consequently, some form of ferrite is ideal for the MCEI element in the present invention. Most preferably, the ferrite is one commercially available from Fair-Rite Products Corp., Wallkill, N.Y., grade 61, having a magnetic permeability of about 125. There are a number of other manufacturers that provide commercial products having a corresponding grade and permeability albeit under different designations.
As an alternative to using a single material that is both magnetically conductive and electrically insulating, the MCEI element can be made from a combination of materials selected and configured to give these properties to the element as a whole. For example, the element can be made from a matrix of particles or fibers of one material that is magnetically conductive and particles of another material that is electrically insulating, wherein the matrix is designed so as to prevent the conduction of electrical currents, while promoting the conduction of a magnetic current. One such material, composed of ferromagnetic metal particles molded in a polymer matrix, is known in the art as “powdered iron.” Also, instead of a matrix, the MCEI element may be formed from laminations of a materials such as a silicon transformer steel separated by an electrically insulating material, such as a ceramic, mineral (mica), or a polymer. Because the induced electric field is always perpendicular to the magnetic field, the chief requirement for the MCEI element is that the magnetic field be accommodated in a direction that wraps around the coil, whereas electrical conduction should be blocked in the circumferential direction, perpendicular to the magnetic field and parallel to the coil.
In accordance with one embodiment of the present invention, the MCEI is formed from a single piece of ferrite of other piece of MCEI material. This can be accomplished by molding, sintering, or machining the ferrite to the desired shape and size. (Prior Art)
As seen in (Prior Art)
For a given application, the transformer diameter is fixed by the diameter of the pipe. The impedance of the transformer, and its desired operating frequency, can be adjusted by two factors: the number of turns in the conductor and the ratio of length to area of the magnetic path, which curls around the conductors. Increasing the number of turns decreases the operating frequency and increases the impedance. Lengthening the magnetic path, or making it narrower, also decreases the operating frequency and increases the impedance. This is accomplished by increasing the depth of the U-shaped trough or by decreasing the thickness of the side-walls. Adjusting the number of turns gives a large increment, while adjusting the dimensions of the trough enables small increments. Accordingly, the invention allows the impedance of the transformer portion of the transmission line to be precisely matched to that of the conductor portion, which is typically in the range of 30 to 120 ohms. Although an insulated copper wire is preferred, other electrically conductive materials, such as silver or copper coated steel, can be used to form the coil 63.
As can be seen in (Prior Art)
As can be seen in (Prior Art)
As can be seen in (Prior Art)
Because the faces 23 and 33 of the pin and box end may need to be machined in the field after extended use, it may preferred to design the troughs in the pin and box end with a shape and size so as to allow the first and second conductive coils to lie in the bottom of the respective troughs and still be separated a distance from the top of the respective first and second sides. As a result, the faces 23 and 33 can be machined without damaging the coils lying at the bottom of the troughs. In this embodiment, this distance is preferably at least about 0.01 inches, more preferably, this distance is at least about 0.06 inches.
An electrical conductor 67 is attached to the coil 63, in (Prior Art)
Alternatively, the conductor can be a twisted pair of wires, although twisted pair generally suffers from higher attenuation than coaxial cable. Twisted pair generally has a characteristic impedance of about 120 ohms, which would provide a desired matching impedance to certain coil configurations. In addition, for certain configurations of drill pipe, there may be limited room at either end of the pipe for a large-diameter coaxial cable. In this case, a short length of twisted pair might provide a small-diameter transition between the coils at the ends of the pipe and a larger-diameter coaxial cable that runs most of the length of the pipe. For lengths of a few feet, the higher attenuation of twisted pair, and its mismatch of impedance to the coaxial cable are of little consequence. However, if desired, the impedance of the twisted pair can be matched to that of the coaxial cable with a small transmission line transformer (balun).
Although the pipe itself could be used as one leg of the current loop, coaxial cable is preferred, and most preferably the conductor loop is completely sealed and insulated from the pipe. It is preferable to select the electrical properties of the conductor so as to match the impedance of the coils to which it is attached. Preferably, the ratio of the impedance of the electrical conductor to the impedance of the first and second electrically conductive coils is between about 1:2 and 2:1. Most preferably, it is close to 1:1.
The preferred data transmission system provides a relatively broad bandwidth. While not wishing to be bound by any particular theory, it is currently believed that this is accomplished by the low number of turns of conductor and the low reluctance of the magnetic path, thus producing a surprisingly low mutual inductance for such a large diameter coil. For a two-turn coil with a 4.75-inch diameter, the mutual inductance of the assembled toroid is about 1 micro Henry. With a 50 ohm resistive load, peak signal transmission is at about 4 MHz, and at power transmission extends from about 1 MHz to about 12 MHz. The inductive reactance is about 65 ohms, and the attenuation is only about 0.35 dB per joint, equivalent to power transmission of about 92 percent. As adjacent segments are assembled, a serial filter is created, which has the effect of reducing the bandwidth. If each individual transformer had a narrow bandwidth, the band-pass of the filter would change as additional segments are added, which would require that each individual element be separately tuned according to its position in the system. Nevertheless, a surprising feature of the invention is that identical segments can be assembled in any arbitrary number of joints while still enabling efficient signal coupling. The 30-joint test described below gave a total attenuation of 37.5 dB (0.018% power transmission), of which 70% was in the coaxial cable itself, which was chosen to have a shield diameter of 0.047 inches. Maximum power transmission was at 4.2 MHz and the bandwidth, at half power, of 2 MHz. Thus a six volt, 90 milliwatt signal resulted in a detected signal, after 30 joints, of 80 mV.
Although possible problems relating to attenuation make it preferable to use an MCEI element in the system of the present invention, the inventors have found that using a coil having five turns or less can still produce a system with sufficient bandwidth to be useful. More preferably, such a system has 2 turns, and most preferably only a single turn 231. This alternative embodiment is shown in (Prior Art)
It is preferred in the alternative embodiment in (Prior Art)
Turning again to the preferred embodiment, and as shown in (Prior Art)
These two holes can be drilled by conventional means. Preferably, they are drilled by a technique known as gun drilling. Preferably, the recesses can be machined and the holes can be drilled in the field, so as to allow for retrofitting of existing drill pipe sections with the data transmission system of the present invention in the field.
As can be seen in (Prior Art)
After exiting the holes 69 and 70, the electrical conductor passes through the interior of the body of the pipe section. Accordingly, it is important to provide the electrical conductor with insulation that can withstand the harsh conditions as well. At present, the preferred material with which to insulate the conductor 67 is PEEK® As shown in (Prior Art)
In addition to the protection provided by an insulator like the tube of PEEK® described above, it is also preferable to apply a coating to add further protection for the electrical conductor 67. Referring to (Prior Art)
(Prior Art)
(Prior Art)
The accelerometer 195 is connected to a circuit board 197, which generates a carrier signal and modulates it with the signal from the accelerometer. (Prior Art)
The circuit board 197 is connected through conductor 199 to a coil in the MCEI element 187 at the bit end of the sub. It then communicates through MCEI element 189, conductor element 191, and MCEI element 193, to the opposite end of the sub, which is adapted to connect to corresponding elements in the drill string. As such, the sub 183 is adapted to communicate with the pin end of a section of drill pipe or some other downhole component.
Many other types of data sources are important to management of a drilling operation. These include parameters such as hole temperature and pressure, salinity and pH of the drilling mud, magnetic declination and horizontal declination of the bottom-hole assembly, seismic look-ahead information about the surrounding formation, electrical resistivity of the formation, pore pressure of the formation, gamma ray characterization of the formation, and so forth. The high data rate provided by the present invention provides the opportunity for better use of this type of data and for the development of gathering and use of other types of data not presently available.
Preferably, the system will transmit data at a rate of at least 100 bits/second, more preferably, at least 20,000 bits/second, and most preferably, at least about 1,000,000 bits/second.
An advantage of the present invention is that it requires relatively low power and has a relatively high preservation of signal. Thus, the system preferably transmits data through at least 10 components powered only by the varying current supplied to one of the first conductive soils in one of the components. More preferably, the system transmits data through at least 20 components powered only by the varying current supplied to one of the first conductive coils in one of the components.
Preferably, the varying current supplied to the first conductive coil in the one component is driving a varying potential having a peak to peak value of between about 10 mV and about 20 V. Preferably, the current loss between two connected components is less than about 5 percent. Put another way, it is preferred that the power loss between two connected components is less than about 15 percent.
It is anticipated that the transmission line of the invention will typically transmit the information signal a distance of 1,000 to 2,000 feet before the signal is attenuated to the point where it will require amplification. This distance can be increased by sending a stronger signal, with attendant increased power consumption. However, many wells are drilled to depths of up to 20,000 to 30,000 feet, which would necessitate use of repeaters to refurbish the signal. Preferably, the amplifying units are provided in no more than 10 percent of the components in the string of downhole components, more preferably, no more than 5 percent.
In the most preferred embodiment of the invention, any source of information along the drill string, such as the bit sub illustrated in (Prior Art)
Although the invention provides a sufficiently broad-band signal to allow simultaneous transmission of information in each direction (full duplex), it is anticipated, because of the attenuation characteristics of the invention, that the most efficient communication will be half duplex, with a signal being sent from one end of the network to the other in one direction before a signal is sent in the opposite direction (half duplex). Alternatively, an asynchronous transmission line might be set up, with, for instance, 80% of the bandwidth reserved for upstream data and 20% for downstream commands. A control computer at the surface will relay a command down-hole requesting that an identified node send a packet of information. Each repeater examines the identifying header in the command packet. If the header matches its own address, it responds; otherwise, it simply relays the packet on down the network in the same direction. In this manner, many smart nodes can share a common transmission line. Any known scheme for collision detection or avoidance may be used to optimize access to the transmission medium.
Other types of data sources for downhole applications are inclinometers, thermocouples, gamma ray detectors, acoustic wave detectors, neutron sensors, pressure transducers, potentiometers, and strain gages.
Communications on the network are made pursuant to a network protocol. Examples of some commercial protocols are ATM, TCP/IP, Token Ring, and Ethernet. The efficiencies of the present system may require a novel protocol as well. A protocol is an established rule on what the data frame is comprised of. The data frame usually includes a frame header, a datagram, and a CRC. The body of the frame may vary depending on what type of datagram is in use, such as an IP datagram. The end of the frame is a CRC code used for error correction. The IP datagram consists of a header and IP datagram data. In an open system, more than one type of datagram is transported over the same communications channel. The header is further broken down into other information such as header information, source IP address and destination IP address, required by the protocol so that each node knows the origin and destination of each data frame. In this manner the downhole network will allow each node to communicate with the sensors and the surface equipment in order to optimize drilling parameters.
Although the primary purpose of the invention is for relaying of information, a limited amount of power can be transmitted along the transmission line. For instance, it may be desirable to have a second class of nodes distributed at intervals between the primary repeaters. The primary repeaters will be powered by batteries or by a device, such as a turbine, which extracts energy from the mud stream. The secondary nodes may incorporate low power circuits to provide local information of secondary importance, using energy from the transmission line itself. They would not constitute repeaters, since they would be in parallel with the existing transmission line. These secondary nodes may, for instance, tap a small amount of energy from the line to keep a capacitor or battery charged, so that when they are queried from the top at infrequent intervals they can send a brief packet of information at full signal strength. Using this principle, it might be possible to house a small low-power secondary node in every section of drill pipe, thereby providing a continuously distributed DLAN.
The following examples are provided by way of illustration and explanation and as such are not to be viewed as limiting the scope of the present invention.
Bench Test. Bench tests stimulating connected pipe joints were conducted. The tests incorporated 30 sets of inductively coupled joints incorporating flexible segmented ferrite MCEI units in steel rings with recesses machined therein, each set being joined together in series by 34 feet of coaxial cable. The coupler consisted of 0.25-inch long by 0.100-inch diameter ferrite cylinders of permeability 125, having an inside diameter of about 0.05 inches, which were ground in half parallel to the cylindrical axis after infiltration with epoxy, bonding to a nylon chord substrate, and bonding into the groove in the steel. This simulated joint was used to characterize system transmission. A 2-volt peak-to-peak sinusoidal signal from a single 50-ohm, 2.5-mW power source energized the coupler of the first joint and produced a 22 mV, signal at last joint, into a 50 ohm load. Peak signal transmission was at 4.3 MHz, with a band width, at half height, of 2 MHz, The average attenuation in each pipe segment was about 1.2 dB, corresponding to about 78% power transmission. About 70% of the attenuation was in the coaxial cable, which had a relatively small shield diameter (0.047 inches). The carrier signal was modulated with both analog and digital signals, demonstrating that that a recoverable, low power, high frequency, 56 kilobaud signal is achievable across 1000 feet of interconnected drill pipe without the aid of an additional power boost or signal restoration.
Drilling test. XT57 tool joints, one a pin end and the other a box-end, were obtained from Grant Prideco, Houston, Tex. The joints had an outside diameter of approximately 7″ and an inside diameter of 4.750 inches, and they were adapted to receive the coupling transducer by machining an annular groove measuring 0.125″.times.0.200″ deep, having a full radius bottom surface of 0.060″, approximately in the center of the 0.550″ wide external and internal secondary shoulders, respectively, of the pin and box ends. 0.500″ internal shoulder was also machined into the pin-end joint approximately 9 inches from the end opposite its secondary shoulder. The machining increased a portion of the internal diameter of the pin end to about 5.250″. A 0.375 inches borehole was gun drilled through the sidewalls of the two joints, parallel to their longitudinal axis. In the pin end, the borehole commenced within the groove and exited the internal shoulder. In the box end, the borehole commenced within the groove and exited the opposite end of the joint. The two joints were welded together, simulating a full-length pipe that normally would be more than 30 feet long. The change in the internal diameter of the welded joints allowed for positioning 30 feet of coaxial cable within the joint so that the test would electrically equivalent to a full length section of pipe. The coupling transducer, having a nominal diameter of 4.700″, comprising a grade 61 ferrite, with a permeability of about 125, obtained from Fair-Rite, was disposed within the annular grooves. The core of the coupler consisted of a segmented annular ferrite ring measuring approximately 0.100″ wide by 0.050″ high having a 0.050-inch diameter groove centrally located on its exposed face. The ferrite segments were attached to a substrate consisting of an epoxy impregnated nylon cord that served as a backing for the ferrite during the manufacturing process. A coil having two loops of 22-gauge (0.025 inch diameter), enamel coated copper magnet wire, was wound within the ferrite groove and held in place with aircraft epoxy. The wire and ferrite assembly were affixed within the grooves in the steel using a thermally cured polyurethane resin. The ends of the copper wire were allowed to extend approximately 0.5 inches beyond the coupler apparatus and were soldered to the conductors of a type 1674A, coaxial cable, 34 feet long, having a characteristic impedance 50 ohms, obtained from Beldon Cable. The cable was protectively sheathed within a thermoplastic PEEK® material obtained from Zeus Products, and the length of the cable was coiled within the hollow portion of the joint assembly and held in place with a polyvinyl chloride (PVC) sleeve.
A drilling test was conducted in a 100 foot well using thirty physically short, electronically full-length joints configured as described above. A seven-inch roller-cone bit sub from Reed Tool was fitted with an accelerometer, an FM modulator, and a battery power supply, which were sealed in a annular insert housed within the crossover sub connecting the drill string with the bit. The joints were assembled so that their respective transducers were concentrically aligned to within approximately 0.010″ of each other. In the test the drill bit drilled a cement plug with and without the aid of a drilling fluid. A 6V peak-to-peak sinusoidal signal (90 mW into 50 ohm) at the bit sub gave a clean 80 mV PP signal (50 ohm load) at the surface, which was 32 inductive couples and approximately 1000 electrical feet above the source signal. The two extra inductive pairs comprised a pair at the accelerometer sub and a rotary pair at the top drive. The audible portion of the accelerometer signal (below 20 kHz) produced an audio signal that enabled the ear to discriminate mud turbulence from drilling activity.
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